It is well known that chlorine dioxide gas is a strong oxidant, and its oxidizing action is effective in sterilization and decomposition of malodorous substances. Therefore, chlorine dioxide has been used in disinfectant, deodorant and the like. Chlorine dioxide is dissolved in water in 20 times its volume of water, to give a yellowish brown aqueous solution. From the viewpoint of handling, it is desirable to use chlorine dioxide in a form of such an aqueous solution. However, when the aqueous solution of chlorine dioxide is brought into contact with air, chlorine dioxide gas is rapidly generated. Therefore, there has been proposed a technique in which stability of chlorine dioxide gas is maintained by dissolving chlorine dioxide gas in an aqueous solution of sodium peroxycarbonate (Na2C2O6), and thus by forming an aqueous solution containing sodium chlorite (NaClO2) as a main component at a retained pH of 9, i.e., what is called a stabilized aqueous solution of chlorine dioxide (see Patent Document 1).
The stabilized aqueous solution of chlorine dioxide is, however, retained at pH 9 (alkali) for the purpose of maintaining stability, as described above. Accordingly, the generation amount of free chlorine dioxide gas having disinfecting and deodorizing effects or the like is extremely low, and thus it is difficult to attain satisfactory disinfecting and deodorizing effects or the like.
Therefore, it has been proposed that, immediately before its use, a stimulant is added to the stabilized aqueous solution of chlorine dioxide, or an acid is added to lower the pH to 7 or less, for generating chlorine dioxide gas. However, with this technique, there arise economical problems that equipments or facilities to implement such processes are required.
In addition, the retention of the generation of chlorine dioxide from the stabilized aqueous solution of chlorine dioxide depends solely on the concentration of the contained chlorine dioxide, and therefore there is a problem which should be fundamentally remedied in that the development of a product having the retention of the generation of chlorine dioxide suitable for intended use is extremely difficult.
In order to solve the above-mentioned problems, there has been proposed a technique in which a mixture prepared by adding a pH adjuster formed of an organic acid, such as citric acid, to chlorite is blended with a solution of chlorine dioxide dissolved therein, to thereby obtain a three-component mixture which can maintain a chlorine dioxide concentration nearly constant for a long term (see Patent Documents 1 and 2). With this technique, the preservation stability of chlorine dioxide can be remarkably enhanced, and the chlorine dioxide concentration can be maintained constant for a long term.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 61-181532
Patent Document 2: Japanese Patent Publication No. 3110724